diff --git a/README.md b/README.md
index 8c57e59..9818e75 100644
--- a/README.md
+++ b/README.md
@@ -189,14 +189,32 @@ encourage your customers to perform an action.
 #                          event. These attributes can be used in your triggers to control who should
 #                          receive the triggered email. You can set any number of data values.
 
-$customerio.track(5, "purchase", :type => "socks", :price => "13.99")
+$customerio.track(5, "purchase", { :type => "socks", :price => "13.99" })
 ```
 
-**Note:** If you want to track events which occurred in the past, you can include a `timestamp` attribute
+**Note:** If you want to track events which occurred in the past, you can pass a `timestamp` keyword argument
 (in seconds since the epoch), and we'll use that as the date the event occurred.
 
 ```ruby
-$customerio.track(5, "purchase", :type => "socks", :price => "13.99", :timestamp => 1365436200)
+$customerio.track(5, "purchase", { :type => "socks", :price => "13.99" }, timestamp: 1365436200)
+```
+
+#### Deduplicating events
+
+You can provide a [ULID](https://github.com/ulid/spec) `id` to deduplicate events. If two events have the same `id`, Customer.io won't process the event a second time.
+
+```ruby
+$customerio.track(5, "purchase", { :type => "socks" }, id: "01BX5ZZKBKACTAV9WEVGEMMVRY")
+
+$customerio.track_anonymous("anon-id", "purchase", { :type => "socks" }, id: "01BX5ZZKBKACTAV9WEVGEMMVRY")
+```
+
+You can also pass `timestamp` as a keyword argument (epoch seconds) instead of including it in the attributes hash:
+
+```ruby
+$customerio.track(5, "purchase", { :type => "socks" }, timestamp: 1561231234)
+
+$customerio.track(5, "purchase", { :type => "socks" }, id: "01BX5ZZKBKACTAV9WEVGEMMVRY", timestamp: 1561231234)
 ```
 
 ### Tracking anonymous events
@@ -211,7 +229,7 @@ Anonymous events cannot trigger campaigns by themselves. To trigger a campaign,
 # name (required)                   - the name of the event you want to track.
 # attributes (optional)             - related information you want to attach to the event.
 
-$customerio.track_anonymous(anonymous_id, "product_view", :type => "socks" )
+$customerio.track_anonymous(anonymous_id, "product_view", { :type => "socks" })
 ```
 
 Use the `recipient` attribute to specify the email address to send the messages to. [See our documentation on how to use anonymous events for more details](https://customer.io/docs/invite-emails/).
@@ -221,7 +239,7 @@ Use the `recipient` attribute to specify the email address to send the messages
 If you previously sent [invite events](https://customer.io/docs/anonymous-invite-emails/), you can achieve the same functionality by sending an anonymous event with `nil` for the anonymous identifier. To send anonymous invites, your event *must* include a `recipient` attribute. 
 
 ```ruby
-$customerio.track_anonymous(nil, "invite", :recipient => "new.person@example.com" )
+$customerio.track_anonymous(nil, "invite", { :recipient => "new.person@example.com" })
 ```
 
 ### Adding a mobile device
diff --git a/lib/customerio/client.rb b/lib/customerio/client.rb
index 078adc5..98e27da 100644
--- a/lib/customerio/client.rb
+++ b/lib/customerio/client.rb
@@ -52,11 +52,11 @@ def unsuppress(customer_id)
       @client.request_and_verify_response(:post, unsuppress_path(customer_id))
     end
 
-    def track(customer_id, event_name, attributes = {})
+    def track(customer_id, event_name, attributes = {}, id: nil, timestamp: nil)
       raise ParamError, "customer_id must be a non-empty string" if empty?(customer_id)
       raise ParamError, "event_name must be a non-empty string" if empty?(event_name)
 
-      create_customer_event(customer_id, event_name, attributes)
+      create_customer_event(customer_id, event_name, attributes, id: id, timestamp: timestamp)
     end
 
     def pageview(customer_id, page, attributes = {})
@@ -66,10 +66,10 @@ def pageview(customer_id, page, attributes = {})
       create_pageview_event(customer_id, page, attributes)
     end
 
-    def track_anonymous(anonymous_id, event_name, attributes = {})
+    def track_anonymous(anonymous_id, event_name, attributes = {}, id: nil, timestamp: nil)
       raise ParamError, "event_name must be a non-empty string" if empty?(event_name)
 
-      create_anonymous_event(anonymous_id, event_name, attributes)
+      create_anonymous_event(anonymous_id, event_name, attributes, id: id, timestamp: timestamp)
     end
 
     def add_device(customer_id, device_id, platform, data = {})
@@ -190,20 +190,24 @@ def create_or_update(attributes = {})
       @client.request_and_verify_response(:put, url, attributes)
     end
 
-    def create_customer_event(customer_id, event_name, attributes = {})
+    def create_customer_event(customer_id, event_name, attributes = {}, id: nil, timestamp: nil)
       create_event(
         url: "#{customer_path(customer_id)}/events",
         event_name: event_name,
-        attributes: attributes
+        attributes: attributes,
+        id: id,
+        timestamp: timestamp
       )
     end
 
-    def create_anonymous_event(anonymous_id, event_name, attributes = {})
+    def create_anonymous_event(anonymous_id, event_name, attributes = {}, id: nil, timestamp: nil)
       create_event(
         url: "/api/v1/events",
         event_name: event_name,
         anonymous_id: anonymous_id,
-        attributes: attributes
+        attributes: attributes,
+        id: id,
+        timestamp: timestamp
       )
     end
 
@@ -216,11 +220,13 @@ def create_pageview_event(customer_id, page, attributes = {})
       )
     end
 
-    def create_event(url:, event_name:, anonymous_id: nil, event_type: nil, attributes: {})
+    def create_event(url:, event_name:, anonymous_id: nil, event_type: nil, attributes: {}, id: nil, timestamp: nil) # rubocop:disable Metrics/ParameterLists
       body = { name: event_name, data: attributes }
-      body[:timestamp] = attributes[:timestamp] if valid_timestamp?(attributes[:timestamp])
+      body[:timestamp] = timestamp if valid_timestamp?(timestamp)
+      body[:timestamp] = attributes[:timestamp] if body[:timestamp].nil? && valid_timestamp?(attributes[:timestamp])
       body[:anonymous_id] = anonymous_id unless empty?(anonymous_id)
       body[:type] = event_type unless empty?(event_type)
+      body[:id] = id unless empty?(id)
 
       @client.request_and_verify_response(:post, url, body)
     end
diff --git a/spec/client_spec.rb b/spec/client_spec.rb
index 27ba3db..bcaa54c 100644
--- a/spec/client_spec.rb
+++ b/spec/client_spec.rb
@@ -360,7 +360,7 @@ def json(data)
         })).
         to_return(status: 200, body: "", headers: {})
 
-      client.track(5, "purchase", type: "socks", price: "13.99")
+      client.track(5, "purchase", {type: "socks", price: "13.99"})
     end
 
     it "copes with arrays" do
@@ -373,7 +373,7 @@ def json(data)
         }).
         to_return(status: 200, body: "", headers: {})
 
-      client.track(5, "event", things: ["a", "b", "c"])
+      client.track(5, "event", {things: ["a", "b", "c"]})
     end
 
     it "copes with hashes" do
@@ -386,7 +386,7 @@ def json(data)
         }).
         to_return(status: 200, body: "", headers: {})
 
-      client.track(5, "event", stuff: { a: "b" })
+      client.track(5, "event", {stuff: { a: "b" }})
     end
 
     it "sends a POST request as json using json headers" do
@@ -402,7 +402,22 @@ def json(data)
       client.track(5, "purchase", data)
     end
 
-    it "allows sending of a timestamp" do
+    it "allows sending of a timestamp via keyword arg" do
+      stub_request(:post, api_uri('/api/v1/customers/5/events')).
+        with(body: json({
+          name: "purchase",
+          data: {
+            type: "socks",
+            price: "13.99"
+          },
+          timestamp: 1561231234
+        })).
+        to_return(status: 200, body: "", headers: {})
+
+      client.track(5, "purchase", {type: "socks", price: "13.99"}, timestamp: 1561231234)
+    end
+
+    it "allows sending of a timestamp via attributes for backwards compat" do
       stub_request(:post, api_uri('/api/v1/customers/5/events')).
         with(body: json({
           name: "purchase",
@@ -415,7 +430,7 @@ def json(data)
         })).
         to_return(status: 200, body: "", headers: {})
 
-      client.track(5, "purchase", type: "socks", price: "13.99", timestamp: 1561231234)
+      client.track(5, "purchase", {type: "socks", price: "13.99", timestamp: 1561231234})
     end
 
     it "doesn't send timestamp if timestamp is in milliseconds" do
@@ -424,13 +439,12 @@ def json(data)
           name: "purchase",
           data: {
             type: "socks",
-            price: "13.99",
-            timestamp: 1561231234000
+            price: "13.99"
           }
         })).
         to_return(status: 200, body: "", headers: {})
 
-      client.track(5, "purchase", type: "socks", price: "13.99", timestamp: 1561231234000)
+      client.track(5, "purchase", {type: "socks", price: "13.99"}, timestamp: 1561231234000)
     end
 
     it "doesn't send timestamp if timestamp is a date" do
@@ -441,13 +455,12 @@ def json(data)
           name: "purchase",
           data: {
             type: "socks",
-            price: "13.99",
-            timestamp: Time.now.to_s
+            price: "13.99"
           }
         }).
         to_return(status: 200, body: "", headers: {})
 
-      client.track(5, "purchase", type: "socks", price: "13.99", timestamp: date)
+      client.track(5, "purchase", {type: "socks", price: "13.99"}, timestamp: date)
     end
 
     it "doesn't send timestamp if timestamp isn't an integer" do
@@ -456,14 +469,61 @@ def json(data)
           name: "purchase",
           data: {
             type: "socks",
-            price: "13.99",
-            timestamp: "Hello world"
+            price: "13.99"
           }
         })).
 
         to_return(status: 200, body: "", headers: {})
 
-      client.track(5, "purchase", type: "socks", price: "13.99", timestamp: "Hello world")
+      client.track(5, "purchase", {type: "socks", price: "13.99"}, timestamp: "Hello world")
+    end
+
+    it "sends an event id for deduplication when provided" do
+      stub_request(:post, api_uri('/api/v1/customers/5/events')).
+        with(body: json({
+          name: "purchase",
+          data: { type: "socks" },
+          id: "01HB4HBDKTFWYZCK01DMRSWRFD"
+        })).
+        to_return(status: 200, body: "", headers: {})
+
+      client.track(5, "purchase", { type: "socks" }, id: "01HB4HBDKTFWYZCK01DMRSWRFD")
+    end
+
+    it "doesn't send id when not provided" do
+      stub_request(:post, api_uri('/api/v1/customers/5/events')).
+        with(body: json({
+          name: "purchase",
+          data: { type: "socks" }
+        })).
+        to_return(status: 200, body: "", headers: {})
+
+      client.track(5, "purchase", { type: "socks" })
+    end
+
+    it "sends a timestamp as a top-level field when provided as keyword arg" do
+      stub_request(:post, api_uri('/api/v1/customers/5/events')).
+        with(body: json({
+          name: "purchase",
+          data: { type: "socks" },
+          timestamp: 1561231234
+        })).
+        to_return(status: 200, body: "", headers: {})
+
+      client.track(5, "purchase", { type: "socks" }, timestamp: 1561231234)
+    end
+
+    it "supports both id and timestamp keyword args together" do
+      stub_request(:post, api_uri('/api/v1/customers/5/events')).
+        with(body: json({
+          name: "purchase",
+          data: { type: "socks" },
+          timestamp: 1561231234,
+          id: "01HB4HBDKTFWYZCK01DMRSWRFD"
+        })).
+        to_return(status: 200, body: "", headers: {})
+
+      client.track(5, "purchase", { type: "socks" }, id: "01HB4HBDKTFWYZCK01DMRSWRFD", timestamp: 1561231234)
     end
 
     context "tracking an anonymous event" do
@@ -489,24 +549,23 @@ def json(data)
           }).
           to_return(status: 200, body: "", headers: {})
 
-        client.track_anonymous(anon_id, "purchase", type: "socks", price: "13.99")
+        client.track_anonymous(anon_id, "purchase", { type: "socks", price: "13.99" })
       end
 
-      it "allows sending of a timestamp" do
+      it "allows sending of a timestamp via keyword arg" do
         stub_request(:post, api_uri('/api/v1/events')).
           with(body: {
             anonymous_id: anon_id,
             name: "purchase",
             data: {
               type: "socks",
-              price: "13.99",
-              timestamp: 1561231234
+              price: "13.99"
             },
             timestamp: 1561231234
           }).
           to_return(status: 200, body: "", headers: {})
 
-        client.track_anonymous(anon_id, "purchase", type: "socks", price: "13.99", timestamp: 1561231234)
+        client.track_anonymous(anon_id, "purchase", { type: "socks", price: "13.99" }, timestamp: 1561231234)
       end
 
       it "raises an error if POST doesn't return a 2xx response code" do
@@ -540,6 +599,19 @@ def json(data)
 
         lambda { client.track_anonymous(anon_id, "") }.should raise_error(Customerio::Client::ParamError)
       end
+
+      it "sends an event id for deduplication when provided" do
+        stub_request(:post, api_uri('/api/v1/events')).
+          with(body: {
+            anonymous_id: anon_id,
+            name: "purchase",
+            data: {},
+            id: "01HB4HBDKTFWYZCK01DMRSWRFD"
+          }).
+          to_return(status: 200, body: "", headers: {})
+
+        client.track_anonymous(anon_id, "purchase", {}, id: "01HB4HBDKTFWYZCK01DMRSWRFD")
+      end
     end
   end